1. Field of the Invention
The present invention relates voice communication and, in particular, to a voice communication method and system in a Ubiquitous Robotic Companion (URC) environment that is capable of establishing a voice communication channel between terminals by using User Datagram Protocol (UDP) and Network Address Translator (NAT) for converting a private Internet Protocol (IP) address to a Public IP address.
2. Description of the Related Art
Ubiquitous Robotic Companion (URC) is a Ubiquitous Network-based Robot system that aims for a robot friend to service people anywhere and anytime through the network. This goal can be achieved by distributing most of robot functions to URC servers and providing intelligence for robots with low prices such that an individual can command a robot and enjoy various URC services.
In the meantime, IP telephony is a voice communication service provided through the Internet. Typically, IP telephony is implemented with the User Datagram Protocol (UDP) to secure real time voice transmission. In order to establish a UDP transport channel, however, both the calling and called terminals are in a public domain in which the terminals are assigned public IP addresses. In a case that the called terminal is located in a private domain, the calling party may know only the public IP address of a Network Address Translator (NAT) enabled router but not the private IP address of the called terminal, resulting in communication channel establishment failure.
In order to solve this problem, a port forwarding technique, in which the ports of the router are forcibly assigned respective private IP addresses, has been used. The port forwarding technique disables automatic port assignment function of the router such that the terminals located in the domain under the control of the same router can communicate with each other with the knowledge of IP addresses matched to the port numbers of the router.
However, the port forwarding technique has a drawback in that the ports of the router (e.g. line sharer and access point (AP)) are assigned with fixed IP addresses, resulting in inefficiency of resource management. Also, the port forwarding technique requires that the terminals are assigned fixed private IP addresses because the use of flexible IP addresses requires frequent update of a mapping table whenever the IP address assigned to each terminal is changed. Accordingly, there has been a need for developing an improved IP telephony method that is capable of establishing a voice channel between terminals assigned private flexible IP addresses.